Update split keyboard docs (#4735)

* Remove unused I2C_MASTER_RIGHT setting

* Update documentation about split keyboard options

docs/config_options.md

@@ -197,8 +197,27 @@ If you define these options you will enable the associated feature, which may in
 
 Split Keyboard specific options, make sure you have 'SPLIT_KEYBOARD = yes' in your rules.mk
 
+### Setting Handedness
+
+One thing to remember, the side that the USB port is plugged into is always the master half. The side not plugged into USB is the slave.
+
+There are a few different ways to set handedness for split keyboards (listed in order of precedence):
+
+1. Set `SPLIT_HAND_PIN`: Reads a pin to determine handedness. If pin is high, it's the left side, if low, the half is determined to be the right side
+2. Set `EE_HANDS` and flash `eeprom-lefthand.eep`/`eeprom-righthand.eep` to each half
+3. Set `MASTER_RIGHT`: Half that is plugged into the USB port is determined to be the master and right half (inverse of the default)
+4. Default: The side that is plugged into the USB port is the master half and is assumed to be the left half. The slave side is the right half
+
 * `#define SPLIT_HAND_PIN B7` 
-  * For using high/low pin to determine handedness, low = right hand, high = left hand. Replace 'B7' with the pin you are using. This is optional and you can still use the EEHANDS method or MASTER_LEFT / MASTER_RIGHT defines like the stock Let's Split uses.
+  * For using high/low pin to determine handedness, low = right hand, high = left hand. Replace `B7` with the pin you are using. This is optional, and if you leave `SPLIT_HAND_PIN` undefined, then you can still use the EE_HANDS method or MASTER_LEFT / MASTER_RIGHT defines like the stock Let's Split uses.
+
+* `#define EE_HANDS` (only works if `SPLIT_HAND_PIN` is not defined)
+  * Reads the handedness value stored in the EEPROM after `eeprom-lefthand.eep`/`eeprom-righthand.eep` has been flashed to their respective halves.
+
+* `#define MASTER_RIGHT`
+  * Master half is defined to be the right half.
+
+### Other Options
 
 * `#define USE_I2C`
   * For using I2C instead of Serial (defaults to serial)
@@ -206,6 +225,20 @@ Split Keyboard specific options, make sure you have 'SPLIT_KEYBOARD = yes' in yo
 * `#define SOFT_SERIAL_PIN D0`
   * When using serial, define this. `D0` or `D1`,`D2`,`D3`,`E6`.
 
+* `#define MATRIX_ROW_PINS_RIGHT { <row pins> }`
+* `#define MATRIX_COL_PINS_RIGHT { <col pins> }`
+  * If you want to specify a different pinout for the right half than the left half, you can define `MATRIX_ROW_PINS_RIGHT`/`MATRIX_COL_PINS_RIGHT`. Currently, the size of `MATRIX_ROW_PINS` must be the same as `MATRIX_ROW_PINS_RIGHT` and likewise for the definition of columns.
+
+* `#define SELECT_SOFT_SERIAL_SPEED <speed>` (default speed is 1)
+  * Sets the protocol speed when using serial communication
+  * Speeds:
+    * 0: about 189kbps (Experimental only)
+    * 1: about 137kbps (default)
+    * 2: about 75kbps
+    * 3: about 39kbps
+    * 4: about 26kbps
+    * 5: about 20kbps
+
 # The `rules.mk` File
 
 This is a [make](https://www.gnu.org/software/make/manual/make.html) file that is included by the top-level `Makefile`. It is used to set some information about the MCU that we will be compiling for as well as enabling and disabling certain features.

quantum/split_common/serial.c

@@ -90,7 +90,7 @@
 
 #ifndef SELECT_SOFT_SERIAL_SPEED
 #define SELECT_SOFT_SERIAL_SPEED 1
-//  0: about 189kbps (Experiment only)
+//  0: about 189kbps (Experimental only)
 //  1: about 137kbps (default)
 //  2: about 75kbps
 //  3: about 39kbps

quantum/split_common/split_util.c

@@ -36,8 +36,7 @@ static void setup_handedness(void) {
     #ifdef EE_HANDS
       isLeftHand = eeprom_read_byte(EECONFIG_HANDEDNESS);
     #else
-      // I2C_MASTER_RIGHT is deprecated, use MASTER_RIGHT instead, since this works for both serial and i2c
-      #if defined(I2C_MASTER_RIGHT) || defined(MASTER_RIGHT)
+      #ifdef(MASTER_RIGHT)
         isLeftHand = !has_usb();
       #else
         isLeftHand = has_usb();